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We study quasiparticle relaxation dynamics in single crystals of the three dimensional Kitaev hyperhoneycomb β-Li₂IrO₃ (LIO) using time-resolved optical pump-probe spectroscopy (OPPS). OPPS is extremely sensitive to subtle changes in the low energy electronic structure and the emergence of new quasiparticles, which can be missed with other probes. For LIO, we show that the photoinduced change in reflectivity is sensitive to several distinct phases upon varying temperature, photoexcitation intensity, and magnetic field applied along the crystallographic b axis. We observe large differences in the relaxation dynamics in the incommensurate spiral phase at low applied fields as compared to the field-induced zig-zag phase at fields above 2.8 Tesla. In addition, OPPS is sensitive to the recently discovered bulk high temperature phase transition at approximately 100 Kelvin. By tracking the evolution of quasiparticle dynamics within this new phase as a function of temperature and field, our results shed light on the nature of this phase as well as its relationship to the known low temperature phases.